Method and apparatus for receiving a universal input voltage in a welding power source

ABSTRACT

A method and apparatus for providing a welding current is disclosed. The power source is capable of receiving any input voltage over a wide range of input voltages and includes an input rectifier that rectifies the ac input into a dc signal. A dc voltage stage converts the dc signal to a desired dc voltage and an inverter inverts the dc signal into a second ac signal. An output transformer receives the second ac signal and provides a third ac signal that has a current magnitude suitable for welding. The welding current may be rectified and smoothed by an output inductor and an output rectifier. A controller provides control signals to the inverter and an auxiliary power controller that can receive a range of input voltage and provide a control power signal to the controller.

This new application is a continuation of, and claims the benefit of thefiling date of, U.S. patent application Ser. No. 08/779,044, filed Jan.6, 1997, entitled Method And Apparatus For Receiving A Universal InputVoltage In A Welding Power Source, which issued on Dec. 14, 1999 as Pat.No. 6,002,103, which is a continuation of, and claims the benefit of thefiling date of, U.S. patent application Ser. No. 08/342,378 filed Nov.18, 1994, entitled Method And Apparatus For Receiving A Universal InputVoltage In A Welding Power Source, which issued on Feb. 11, 1997, asPat. No. 5,601,741.

FIELD OF THE INVENTION

This invention generally relates to power sources. More particularly,this invention relates to inverter power sources employed in welding,cutting and heating applications.

Power sources typically convert a power input to a necessary ordesirable power output tailored for a specific application. In weldingapplications, power sources typically receive a high voltage alternatingcurrent (VAC) signal and provide a high current output welding signal.Around the world, utility power supplies (sinusoidal line voltages) maybe 200/208V, 230/240V, 380/415V, 460/480V, 500V and 575V. These suppliesmay be either single-phase or three-phase and either 50 or 60 Hz.Welding power sources receive such inputs and produce an approximately10-40 volt dc high current welding output.

Welding is an art wherein large amounts of power are delivered to awelding arc which generates heat sufficient to melt metal and to createa weld. There are many types of welding power sources that provide powersuitable for welding. Some prior art welding sources are resonantconverter power sources that deliver a sinusoidal output. Other weldingpower sources provide a squarewave output. Yet another type of weldingpower source is an inverter-type power source.

Inverter-type power sources are particularly well suited for weldingapplications. An inverter power source can provide an ac square wave ora dc output. Inverter power sources also provide for a relatively highfrequency stage, which provides a fast response in the welding output tochanges in the control signals.

Generally speaking, an inverter-type power source receives a sinusoidalline input, rectifies the sinusoidal line input to provide a dc bus, andinverts the dc bus and may rectify the inverted signal to provide a dcwelding output. It is desirable to provide a generally flat, i.e. verylittle ripple, dc bus. Accordingly, it is not sufficient to simplyrectify the sinusoidal input; rather, it is necessary to also smooth,and in many cases alter the voltage of, the input power. This is calledpreprocessing of the input power.

There are several types of inverter power sources that are suitable forwelding. These include boost power sources, buck power sources, andboost-buck power sources, which are well known in the art.

Generally, a welding power source is designed for a specific powerinput. In other words, the power source cannot provide essentially thesame output over the various input voltages. Further, components whichoperate safely at a particular input power level are often damaged whenoperating at an alternate input power level. Therefore, power sources inthe prior art have provided for these various inputs by employingcircuits which can be manually adjusted to accommodate a variety ofinputs. These circuits generally may be adjusted by changing thetransformer turns ratio, changing the impedance of particular circuitsin the power source or arranging tank circuits to be in series or inparallel. In these prior art devices, the operator was required toidentify the voltage of the input and then manually adjust the circuitfor the particular input.

Generally, adapting to the various voltage inputs in the prior artrequires that the power source be opened and cables be adjusted toaccommodate the particular voltage input. Thus, the operator wasrequired to manually link the power source so that the appropriateoutput voltage was generated. Operating an improperly linked powersource could result in personal injury, power source failure orinsufficient power.

Prior art devices accommodated this problem by configuring the powersource to operate at two different VAC input levels. For example, U.S.Pat. No. 4,845,607, issued to Nakao, et al. on Jul. 4, 1989, discloses apower source which is equipped with voltage doubling circuits that areautomatically activated when the input is on the order or 115 VAC, andwhich is deactivated when the input is on the order of 230 VAC. Suchsources are designed to operate at the higher voltage level, with thevoltage doubling circuit providing the required voltage when the inputvoltage is at the lower level. This type of source, which uses a voltagedoubling circuit, must use transistors or switching devices as well asother components capable of withstanding impractical high power levelsto implement the voltage doubling circuit. Further, the circuitryassociated with the voltage doubling circuit inherently involves heatdissipation problems. Also, the voltage doubling circuit type of powersource is not fully effective for use in welding applications. Thus,there exists a long felt need for a power source for use in weldingapplications which can automatically be configured for various VAC inputlevels.

Welding power sources are generally known which receive a high VACsignal and generate a high current dc signal. A particularly effectivetype of the power source for welding applications which avoids certaindisadvantages of the voltage doubling circuit type of power sourcegenerally relies on a high frequency power inverter. Inverter powersources convert high voltage dc power into high voltage AC power. The ACpower is provided to a transformer which produces a high current output.

Power inverters for use over input voltage ranges are generally known inthe art. For example, a power inverter which is capable of using twoinput voltage levels is disclosed in U.S. Pat. No. 3,815,009, issued toBerger on Jun. 4, 1974. The power inverter of that patent utilizes twoswitching circuits; the two switching circuits are connected seriallywhen connected to the higher input voltage, but are connected inparallel to account for the lower input voltage. The switching circuitsare coupled to each other by means of lead wires. This inverter issusceptible to operator errors in configuring the switching circuits forthe appropriate voltage level, which can result in power sourcemalfunction or human injury.

Other prior art welding sources that improved upon manual linkingprovided an automatic linkage. For example, the Miller Electric AutoLinkis one such power source and is described in U.S. Pat. No. 5,319,533incorporated herein by reference. Such power sources test the inputvoltage when they are first connected and automatically set the properlinkage for the input voltage sensed. Such welding power sources, ifportable, are generally inverter-type power sources, and the method bywhich linking is accomplished is by operating the welding power sourceas two inverters. The inverters may be connected in parallel (for 230V,for example) or in series (e.g., for 460V). Such arrangements generallyallow for two voltage connection possibilities. However, the highervoltage must be twice the lower voltage. Thus, such a power sourcecannot be connected to supplies ranging from 230V-460V to 380V-415V or575V.

A 50/60 Hz transformer could be used to provide multiple paths forvarious input voltages. It would, however, have the disadvantage ofbeing heavy and bulky compared to an inverter-type welding power sourceof the same capacity. In addition, if it was automatically linked as inthe Miller AutoLink example given above, it would have to have linkapparatus for each voltage. Such an automatic linkage would becomplicated and probably uneconomical for the range of voltagescontemplated by this invention. Thus, it is unlikely that prior artpower sources that automatically select the proper of two input voltagesettings will accommodate the full range of worldwide electrical inputpower. This shortcoming may be significant in that many welding powersources are purchased to be transportable from site to site. The abilityto automatically adapt to a number of input power voltage magnitudes isthus advantageous.

It is, therefore, one object of this invention to provide a weldingpower source that receives any of the above-mentioned input voltages, orany other input voltage, without the need of any linkages, whethermanual or automatic. Additionally, it is desirable to have such awelding power source that incorporate inverter technology and withoutusing high power 50/60 Hz transformers.

SUMMARY OF THE INVENTION

The present invention is a power source that is capable of receiving anyinput voltage over a wide range of input voltages. The power sourceincludes an input rectifier that rectifies the ac input into a dcsignal. A dc voltage stage converts the dc signal to a desired dcvoltage and an inverter inverts the dc signal into a second ac signal.An output transformer receives the second ac signal and provides a thirdac signal that has a desired current magnitude. Although not necessary,the output current may be rectified and smoothed by an output inductorand an output rectifier. A controller provides control signals to theinverter and an auxiliary power controller is capable of receiving arange of input voltages and provides a control power signal to thecontroller.

A method for providing a welding current includes rectifying an ac inputand providing a first dc signal. The first dc signal is then convertedinto a second ac signal. Then the second ac signal is converted into athird ac signal that has a current magnitude suitable for welding. Thewelding current may then be rectified and smoothed to provide a dcwelding current and an auxiliary power signal is supplied at apreselected control power signal voltage, regardless of the magnitude ofthe ac input signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the preferred embodiment of the presentinvention;

FIG. 2 is a detailed diagram of the input rectifier of FIG. 1;

FIG. 3 is a detailed diagram of the boost circuit of FIG. 1;

FIG. 4 is a detailed diagram of the pulse width modulator of FIG. 1; and

FIG. 5 is a control circuit for the auxiliary power controller of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, the welding power source 100 includes an inputrectifier 101, a boost circuit 102, a pulse-width modulator 103, acontroller 104, an auxiliary power controller 105, a pair of storagecapacitors C3 and C7, and their associated protective resistors R4 andR10, and output transformer T3, an output inductor L4, feedback currenttransformers T4 and T6, feedback capacitors and resistors C13, C14, R12and R13, and output diodes D12 and D13 to provide a welding outputcurrent on welding output terminals 108. A cooling fan 110, a frontpanel 111, and a remote connector 112 are also shown schematically.

In operation, power source 100 receives a three-phase line voltage oninput lines 107. The three-phase input is provided to input rectifier101. Input rectifier 101 rectifies the three-phase input to provide agenerally dc signal. A 10 microfarad capacitor C4 is provided for highfrequency decoupling of the boost circuit. The dc signal has a magnitudeof approximately 1.35 times the magnitude of the three-phase input. Thedecoupled dc bus is provided to boost circuit 102. As will be describedin greater detail below, boost circuit 102 processes the dc bus providedby input rectifier 101 to provide a dc output voltage having acontrollable magnitude. In the preferred embodiment the output of boostcircuit 102 will be approximately 800 volts, regardless of the inputvoltage.

The output of boost circuit 102 is provided to pulse-width modulator103, where the dc bus is inverted and pulse-width modulated to provide acontrollable signal suitable for transforming into a welding output.Controller 104 is a main control board such as that found in manyinverter-type welding power sources. The main control board provides thecontrol signals to pulse-width modulator 103, to control the frequencyand pulse-width of pulse-width modulator 103. Input rectifier 101,pulse-width modulator 103, controller 104 and output transformer T3 arewell known in the art.

The output of pulse-width modulator 103 is provided to an outputtransformer T3, which, transforms the output of PWM 103 to provide avoltage and current suitable for welding. Transformer T3 has a centertap secondary and is provided with a turns ratio of 32 turns on theprimary to 5 turns on each half for the center tap secondary. Of course,other transformers may be used. The alternating output of transformer T3is rectified and smoothed by an output inductor L4 and output diodes D12and D13. Inductor L4 has an inductance sufficient to provide desirablewelding characteristics, such as, for example, in a range of 50-150microhenrys.

Auxiliary power controller 105 receives the input line voltage andconverts that voltage to a 18 volt dc control signal. The 18 voltcontrol signal is created regardless of the input voltage, and isprovided to boost circuit 102. Boost circuit 102 uses the 18 voltcontrol signal to control its switching frequency and the magnitude ofits output. Auxiliary power controller 105 also provides a 48 voltcenter tap ac power signal to controller 104.

Front panel 104 is shown schematically and is used to convey operatingstatus to the user, as well as receive inputs as to operatingparameters. Similarly, remote connector 112 is shown schematically andis used to receive inputs as to operate parameters.

Generally speaking, at power-up a three phase input is provided on inputlines 107. A plurality of initially open contactors 115 isolates theinput power from input rectifier 101. However, the input power isprovided to auxiliary power controller 105. As will be described ingreater detail below, auxiliary power controller 105 determines themagnitude of the input power, and opens or closes a number of contactsto provide a 48 volt center tap ac output to controller 104, regardlessof the input. The contacts are closed and opened in such a way as toprovide safeguards against underestimating the magnitude of the inputvoltage, and thus protecting the circuit components. Also, auxiliarypower controller 105 provides an 18 volt dc control signal to boostcircuit 102, regardless of the magnitude of the input.

After the voltage level has been properly determined by closing theproper contacts controller 104 causes contacts 115 to be closed, thusproviding power to input rectifier 101. Input rectifier 101 includes aprecharge circuit to prevent a resonant overcharge from harmingcapacitors C3 and C7 and to avoid excessively loading of the inputsource. A signal received by input rectifier 101 from a tap ontransformer T3 turns on an SCR (described in more detail below). Theconducting SCR bypasses input current around the precharge resistors.

The output of input rectifier 101 is provided to boost circuit 102.Boost circuit 102 is well known in the art and integrated circuitcontrollers for boost circuits may be purchased commercially. Inoperation boost circuits 102 senses the voltage at its inputs and itsoutputs. As will be described in more detail later and IGBT (or otherswitching element) is switched on and off at a frequency and duty cycle(or pulse width) to obtain a desired output voltage. In the preferredembodiment the desired output voltage is approximately 800 volts.

Boost circuit 102 thus provides an output of about 800 volts to 800microfarad electrolytic capacitors C3 and C7, and have 45K ohm bleederand balancing resistors R4 and R7 associated therewith. Capacitors C3and C7 thus acts as a dc link for PWM 103.

PWM 103 receives a generally constant 800 dc signal and modulates it toprovide, after transformation, rectification and smoothing, a weldingoutput at a user selected magnitude. PWM 103 modulates its input inaccordance with control signals received from controller 104. PWM 103also receives a 25 volt dc power signal from controller 104. Such a PWMis well known and PWM 103 may be purchased commercially as a singlemodule.

The output of PWM 103 is provided to output transformer T3 and whichtransforms the relatively high voltage, low current signal to a voltagesuitable for use in welding. The output of transformer T3 is rectifiedby diodes D12 and D13, and smoothed by output inductor L4. Thus, agenerally constant magnitude dc welding output is provided on weldingoutputs 108.

Current transformers T4 and T5, provide feedback signals to controller104, snubber capacitors C13 (0.1 microfarads) and C14 (0.022microfarads), and snubber resistors R12 (12 ohms) and R13 (47 ohms)suppress voltage transients associated with recovery of D12 and D13.Controller 104 compares the feedback signals to the desired weldingcurrent, and appropriately controls PWM 103 to adjust its switchingpulse width if necessary.

Referring now to FIG. 2, the preferred embodiment for input rectifier101 is shown in detail and includes a full wave bridge comprised ofdiodes D4, D5, D6, D9, D10 and D11. The bridge rectifies the three phaseinput to provide a signal having a magnitude of about 1.35 times theinput voltage magnitude. A pair of 50 ohm resistors R1 and R2 areprovided to precharge capacitors C4, C3 and C7 (shown in FIG. 1) uponstart up. This prevents a sudden surge of current from being dumped intocapcitors C4, C3 and C7.

After the precharge is completed an SCR Q1 is turned on via a signalfrom a tap on output transformer T3 (also in FIG. 1). The signal fromtransformer T3 is provided to the gate of SCR Q1 via a current limitingresistor R6 and capacitor C6. A recovery diode D7 and snubber resistorR5 are provided across the gate of SCR Q1. SCR Q1 shunts the resistorsand allows the maximum current flow to inductor L2 of boost circuit 102.

A plurality of varistors RV1-RV3 are provided to suppress line spikes.Additional varistors (not shown) may be provided between D9-D11 andground to further suppress spikes.

As one skilled in the art will readily recognize, other circuits andcircuit elements will accomplish the function of input rectifier 101.

Referring now to FIG. 3, the details of one embodiment of boost circuit102, which operates in a manner well known in the art, is shown.Generally speaking, boost circuit 102 provides an output voltage that isequal to the input voltage divided by one minus the duty cycle of aswitch IGBT1 in boost circuit 102.

Thus, if the switch IGBT1 is off 100% of the time the output voltage(the dc link voltage) is equal to the input voltage (from capacitor C4and input rectifier 101). In one embodiment the lowest input is about200 volts, and the desired output (dc link voltage) is 800 volts, thusthe upper limit for the “boost” is about 400%, and requires a duty cycleof about 75%.

The operation of a boost circuit should be well known in the art andwill be briefly described herein. When switch IGBT1 is turned on,current flows through an inductor L2 to the negative voltage bus, thusstoring energy in inductor L2. When switch IGBT1 is subsequently turnedoff, the power is returned from inductor L2 through a diode D1 and a 14microhenry saturable reactor L1 to the dc link. The amount of energystored versus returned is controlled by controlling the duty cycle inaccordance with the formula stated above. In order for the boost circuitto operate properly inductor L2 must have continuous current, thereforeinductor L2 should be chosen to have a large enough inductance to have acontinuance current over the range of duty cycles. In one embodimentinductor L2 is a 3 millihenry inductor. The remaining elements of boostcircuit 102 include a 0.0033 microfarad capacitor C1, a diode D3, a 1ohm resistor R3, a 50 ohm resistor R6, a diode D8, a 50 ohm resistor R7and a 0.1 microfarad capacitor C8 which are primarily snubbers and helpthe diode recover when switch IGBT1 is turned on.

Boost circuit 102 includes an IGBT driver 301 that controls the dutycycle of switch IGBT1. Driver 301 receives feedback signals indicativeof the output voltage and the input current, and utilizes thisinformation to drive switch IGBT1 at a duty cycle sufficient to producethe desired output voltage.

In one embodiment, boost circuit 102 includes a shunt S1 (shown in FIG.1). Shunt S1 provides a feedback signal that is the current flowing inthe positive and negative buses. A Unitrode power factor correction chipis used to implement boost circuit 102 in the preferred embodiment andrequires average current flow as an input. In response to thisinformation and the dc link voltage, driver 301 turns switch IGBT1 onand off.

As one skilled in the art will readily recognize, other circuits andcircuit elements will accomplish the function of boost circuit 102.

As stated above, the output of boost circuit 102 is provided tocapacitors C3 and C7 (FIG. 1) and is the dc link voltage. In oneembodiment the dc link voltage is 800 volts, as determined by theswitching of switch IGBT1. In the preferred embodiment, using thecomponent values described herein the dynamic regulation of the dc linkvoltage is 80 volts from full load to no load. Static regulation isabout a +/−2 volts, with a ripple of about +/−20 volts.

The dc link voltage is provided to pulse width modulator 103. PWM 103 isa standard pulse with modulator and provides a quasi-square wave outputhaving a magnitude equal to the magnitude of the input, as would anyother PWMs. Thus, the output of PWM 103 is about +400 volts to −400volts for an 800 volt peak to peak centered about zero.

PWM 103 includes a pair of switches Q3 and Q4 (preferably IGBTs) and apulse width driver 401. Driver 401 receives feedback from currenttransformers T1 and T2, and receives control inputs from controller 104.In response to these inputs driver 401 provides gate signals to switchesQ3 and Q4, thereby modulating the input signal. A capacitor C2 (4microfarad) a capacitor C9 (4 microfarad) are provided between the dclink and the output transformer T3. A capacitor C5 (0.0022 microfarad),resistor R11 (50K ohm) and resistor R9 (50K ohm) are snubber circuits.

As one skilled in the art will readily recognize, other circuits andcircuit elements will accomplish the function of PWM 103.

The output of PWM 103 is provided to transformer 103, and the current intransformer 103 is determined by the modulation of PWM 103. As statedabove, the output of transformer T3 is rectified by diodes D12 and D13and is smoothed by inductor L4. The dc output current is fairly flat;the ripple at full load (300 amps) is about 12 amps peak to peak. Atfull load the duty cycle of each switch Q3 and Q4 of PWM 103 would beabout 20-35% (40-70% overall duty cycle).

In an alternative embodiment the output of PWM 103 may be rectified byother output rectifiers such as a synchronous rectifier (cycloconverter)that provides an ac output signal at a frequency less than or equal tothe frequency of the output of PWM 103. Other output circuits, includinginverters, that provide a welding current may also be used.

Referring again to FIG. 1, controller 104 is connected to currenttransformers T4 and T5, which provide feedback information. Controller104 receives power from auxiliary power controller 105 and provides asone of its output the driver control for the PWM driver. It alsoincludes an over voltage protection sense which monitors the voltagecoming out of input rectifier 101. If the voltage from input rectifier101 is dangerously high controller 104 causes contactors 115 to open, toprotect circuit components. According to one embodiment 930 volts dc isthe cut off point for what is considered to a dangerously high voltage.

As may be seen from the above description, welding power source 100receives an input voltage and provides a welding output. Regardless ofthe magnitude of the input voltage boost circuit 102 boosts the inputvoltage to a desired (800 volts e.g.) level. Then PWM 103 modulates thesignal to provide an appropriate level of power, at 800 volts, totransformers T3.

The above arrangement is satisfactory for any input voltage, however,there must be some mechanism to provide control voltages at the properlevel. As will be described below, auxiliary power controller 105performs that function, and the embodiment thereof is shownschematically in FIG. 5.

With reference now to FIG. 5, a plurality of connectors J1, J2, J3 andJ4 are shown. An 18 volt dc control voltage output is provided onconnector J1 to boost circuit 102 (shown on FIG. 1). As will bedescribed in greater detail below, the 18 volt dc control signal isprovided regardless of the magnitude of the input voltage. Connector J2feeds power back to auxiliary power controller 105 for internal use.Connector J3 connects the input ac voltage to appropriate taps on atransformer T7 (FIG. 1) to provide a 30 volt ac signal to remoteconnector 112 (FIG. 1). Similarly, a 48 volt center tap ac signal isprovided to controller 104. Controller 104 uses the 48 volt center tapac signal to generate dc control signals and to power fan 110. ConnectorJ4 of auxiliary power controller 105 is connected via a user controlledon/off switch S4 to the input power lines (FIG. 1).

Auxiliary power controller 105 controls the connections to taps on theprimary of an auxiliary power transformer T7. Transformer T7 is a 200 VAtransformer whose primaries are connected to auxiliary power controller105 as described above with reference to connector J2 and J3. Severaltaps on its secondary are connected to controller 104 and the remainingsecondary taps are connected to remote connector 112.

Referring again to FIG. 5, the taps on J3 are associated with thefollowing voltages: 575, 460, 380, 230 volts, and the return, beginningat the uppermost tap and proceeding downward. As will be describedbelow, when auxiliary power controller 105 selects the appropriate tapfor a given input voltage, transformer T7 will provide a 48 volt centertap ac signal on its secondary for use by controller 104.

As may be seen on FIG. 5, the ac input is received on connector J4 andprovided (via a fuse F1, and a pair of 4.7 ohm resistors R18 and R19) toa series of relays K2B, K1B, K3C and K3B that determines the tap onconnector J3 selected for the output. When 575 volts are present at theinput relays K2B and K3C should be to the right. Then the input isconnected across the upper and lower most taps on connector J3. Thesetaps are connected to the appropriate taps on transformer T7 such thatthe output of transformer T7 that is provided to controller 104 isapproximately 48 volts center tap when 575 volts are provided to theprimary of transformer T7.

When 460 volts are present at the input relay K2B should be to the left,and relay K1B should be to the right. This connects the ac input to thesecond uppermost and the lowest taps on connector J3. The remainingvoltages are similarly accommodated. A pair 0.15 microfarad capacitorsC13 and C14 are provided for snubbing and spike suppression as theprimaries of transformer T7 are switched.

In operation the circuitry on the left side of FIG. 5 determines theinput voltage, and sets the relays for that voltage. At start up therelays are as shown in FIG. 5 and are suitable for an input voltage of575 volts. Because this is the highest possible input voltage, allcomponents will be protected, i.e. either the voltage is properlyselected, or the input voltage is less than the component designcapabilities. If auxiliary power controller 105 determines that 575volts are in fact present, the relays will remain as shown. However, ifauxiliary power controller 105 determines that less than 575 volts arepresent, the state of relay K2B will be changed (to be to the left), sothat the output is appropriate for a 460 volt input.

This process is repeated, always stepping down to the next highestvoltage, until the appropriate input voltage is sensed. In this mannerthe components in controller 104 will be protected from a dangerouslyhigh voltage being applied to controller 104.

The voltage for sensing is provided to auxiliary power controller 105via connector J2, which is connected to secondary taps on transformerT7. Thus, if the tap selected on connector J3 was not correct, then thevoltage on connector J2 will be too low, and auxiliary power controller150 will select the appropriate relay setting to step down to the nextvoltage level. As stated above, the stepping down continues until theproper voltage is sensed on connector J2.

The input from connector J2 is provided to a rectifier comprised ofdiodes CR1, CR2, CR3 and CR4. These diodes rectify the ac signal andprovide it to a pair of 220 microfarad smoothing capacitors C1 and C2.The rectified voltage is +/−18 volts if the proper tap on connector J3is selected. If the incorrect tap is selected the voltage will be lessthan +/−18 volts, but will be referred to as nominally +/−18 volts. Thenominal +/−18 volt supply is provided at other locations throughout theauxiliary power controller 105 circuit, including to a 30 volt zenerdiode CR7, used to determine if the proper tap on connector J3 has beenselected.

Auxiliary power controller 105 determines if 575 volts is present on theinput using the following components: zener diode CR7, a 10 microfaradcapacitor C9, a pair of gates U2B and U2C configured as darlingtondrivers for a winding K2A of relay K2, a 10K ohm resistor RN2A, a 10Kohm resistor RN2B, a 820 ohm resistor R9, and a diode U3B. Gates U2B andU2C are also used as sensing devices and have a threshold of about 4volts (relative to their reference voltages) on the input (pin 1) ofgate U2B pin 1.

Initially, gate U2B has a LOW output and is referenced to nominal −18volts. Gate U2B will not switch states so long as the input is at least4 volts greater than its reference voltage (nominally −18 volts relativeto ground). In operation the nominal +18 volts will be provided to diodeCR7 and the nominal −18 volt signal is applied to a 10 microfaradcapacitor C9. As a result of the 30 volt zener drop, the input to gateU2B will be at −12 volts (relative to ground) if the proper tap has beenselected. If 575 volts are present at the input, there will be 6 voltsrelative to the reference voltage (−18 volts) at the input to op ampU2B, and the output state of gate U2B of gate U2B will remain low. Solong as the output of U2B remains low the current will not flow in thewinding of relay K2 and relay K2B will remain as shown in FIG. 5.

However, if only 460 volts are present on the input and the relays areas shown in FIG. 5 (as they will be at power up), then the nominal +/−18volts will actually be +/−14.4 volts. Thus, 28.8 volts are appliedacross zener diode CR7 and capacitor C9. Given the 30 volt zener drop,−14.4 volts will be applied to the input of gate U2B. Because this isalso the reference voltage for gate U2B, the threshold is crossed, andthe output of gate U2B will change states. Current will then flow in thewinding of relay K2 and relay K2B will change states, configuring the J3taps for 460 volts. If less than 460 volts is present at the input thesame result will occur.

The sensing and stepping down to 380 volts and 230 volts occur in asimilar manner using similar components. Referring to FIG. 5, the senseand step down circuit to 380 volts include a 100 ohm resistor R17, apair of 10K ohm resistors RN2C and RN2D, and 820 ohm resistor R8, adiode U3C, a 10 microfarad capacitor C6, a pair of gates U2D and U2E,and a winding K1A for relay K1. A relay K2C is provided to prevent relayK1 from changing states before the step down to 460 volts occurs. In themanner described above with respect to the step down to 460 volts, thecurrent will be provided to winding K1A of relay K1 if less than 460volts is provided at the input. This will cause relay K1B to move to theleft position and connect the tap on J3 associated with a 380 voltinput.

The circuitry associated with the step down to 230 volts includes a 100ohm resistor R16, a pair of 10K ohm resistors RN1A and RN1B, and 820 ohmresistor R11, a diode U3E, a pair of gates U2F and U2G, a winding K3Afor relay K3, relay K1C, diode CR6 and zener diode CR4. A relay K1C isprovided to prevent relay K3 from changing states before the step downto 380 volts occurs. The step down to 230 volts operates in the samemanner as the step down to 380 volts and 460 volts as described above.If less than 380 volts is applied on the connector J4 inputs, gates U2Fand U2G will cause current to flow through winding K3A of relay K3. Thiswill cause relay K3B to move to the left and connect the tap on J3 for230 volts to the ac input.

Thus, as may seen from the above description, the circuitry of auxiliarypower controller 105 senses the ac input voltage and connects theappropriate tap on the auxiliary power transformer T7 to the ac inputvoltage. As may be seen from the above discussion, this is done in amanner which protects components by assuming the voltage is, upon startup, the highest possible voltage. If the voltage is less than thehighest possible voltage, the next lowest voltage will then be assumed.This process is repeated until the actual voltage is obtained.

In the event that the ac input is 230 volts, at start up there will notbe sufficient power from the nominal +/−18 volt signal to drive therelays because the tap associated with 575 volts on connector J3 isselected at start up. To compensate for this, circuitry that boosts thevoltage supplied on connector J2 is provided. This circuitry includes a1 millihenry inductor L1, a switch Q4, a timer U1, a switch Q2, a switchQ1, and a switch TIP120. Also included are associated circuitryincluding a 22 ohm shunt resistor R13, a 1K resistor R5, a 10K resistorR12, a 10K resistor R14, a 2.2K resistor R4, a 1K resistor R6, a 1Kresistor R2, a 20K resistor R3, a 200 ohm resistor R7, a 10K resistorRN1D, a 4.7K resistor R10, a 470 picofarad capacitor C4, a 0.001microfarad capacitor C3, a 0.1 microfarad capacitor C5, a 220 microfaradcapacitor C11, a 220 microfarad capacitor C12, a diode CR12, a diodeCR8, a zener diode CR10, a diode CR5, and a zener diode CR11.

The boost power source circuitry operates as a typical boost circuit.The boost is provided by inductor L1 and switch Q4. During the timeswitch Q4 is ON, current flows through inductor L1, shunt resistor R13and switch Q4 to the negative voltage supply. During this time, energyis stored in inductor L1. When switch Q4 is OFF, the energy stored ininductor L1 is returned to the positive voltage supply (+B) throughdiode CR12. By appropriate timing of the turning ON and OFF of switchQ4, a desired voltage may be obtained. Timer chip U1 is used to providethe ON/OFF gate signals to switch Q4 and is an LM555 timer. When thevoltage on resistor R13 becomes sufficiently high, it will trip theinput on U1, which in turn will cause the output of timer U1 to turnswitch Q4 OFF.

Initially, switch Q4 is in the ON position and current increases andeventually reaches the point where the voltage on resistor R13 issufficiently high to trip the threshold on timer U1 through resistorR12. Thus, switch Q4 will remain ON for a length of time sufficient tobuild up enough energy to, when it is turned OFF, raise the nominal+/−18 volts to a level sufficient to drive the relays.

Switches Q2 and Q1 enable or disable timer U1 when the taps on connectorJ3 are such that the nominal +/−18 volts signal is actually +/−18 volts.When switch Q2 is turned OFF, timer U1 is disabled through its VCCinput. Also, switch TIP120 is a linear regulator. When the nominal +18volt supply is insufficient to drive the relay, switch TIP120 willprovide the boost source to drive the relays. When the nominal +18voltage is sufficient to drive the relay, switch Q2, timer U1 and switchQ4 are turned off. The +18 volt supply is coupled through L1 and CR12 toregulator TIP120; the +B boost supply is then fed directly by thesufficiently high +18 volt supply. The TIP120 regulator regulates relaysupply at 24 volts relative to the −18 volt supply.

In addition to the circuitry above, circuitry is provided that protectsin the event of an overvoltage. This circuitry includes a switch Q5, agate U2A, a 100 ohm resistor R15, a 10K ohm resistor RN3A, a 10K ohmresistor RN3B, a 10K ohm resistor RN3C, a 10 microfarad capacitor C10,diodes CR14 and U3H, and 10 volt zener diode CR13. An overvoltage occurswhen the tap selected on connector J3 correspond to a voltage less thanthe voltage at the ac input. This may occur when either the incorrecttap has been selected or when a temporarily high voltage is provided atthe ac input.

In the event an overvoltage occurs, the voltage at the node common todiodes CR13 and CR7 will rise to a voltage greater than 14 volts withrespect to the nominal −18 volt signal. This causes the low side ofdiode CR13 to be greater than 4 volts with respect to the nominal −18volt signal, and the input of U2A will change from an input low state toan input high state. When the input of U2A changes from low to high, theoutput will change from an output high state to an output low state. Theoutput low state of U2A will bring the relay supply voltage to a virtual0 through diodes U3H and CR14. This causes the relays to return to thestate shown in FIG. 2, which accommodates the highest voltage possible(575 volts). At that time the previously described tap selection processstepping from the 575 to 460 to 380 to 230 taps begins again until thecorrect tap is selected to match the input voltage received on connectorJ4. Accordingly, the components of controller 104 will be protected.

Other modifications may be made in the design and arrangement of theelements discussed herein without departing from the spirit and scope ofthe invention as expressed in the appended claims.

I claim:
 1. A welding, cutting or heating power source capable ofreceiving a range of input voltages, comprising: an input rectifierconfigured to receive an ac input and to provide a first dc signal; aconverter configured to receive the first dc signal and to provide aconverter output, and configured to receive at least one control input;an output transformer configured to receive the converter output and toprovide a third ac signal having a current suitable for welding, cuttingor heating; an output circuit configured to receive the third ac signaland to provide a welding signal; and a controller, including a powerfactor correction circuit, configured to provide at least one controlsignal to the converter.
 2. The apparatus of claim 1, further includingan auxiliary power source capable of providing a control power signal ata preselected control signal voltage, regardless of the magnitude of theac input signal.
 3. The apparatus of claim 2, further including anauxiliary transformer with a plurality of primary taps, wherein theauxiliary power controller is in electrical communication with theplurality of primary taps.
 4. The apparatus of claim 1, wherein theconverter includes a boost circuit.
 5. The apparatus of claim 1, whereinthe converter includes a pulse width modulator.
 6. The apparatus ofclaim 1, wherein the range of input voltages is 230 volts to 575 volts.7. The apparatus of claim 1 wherein the output circuit includes arectifier.
 8. The apparatus of claim 1 wherein the output circuitincludes a cycloconverter.
 9. A method of providing a welding, cuttingor heating current from a range of input voltages, comprising:converting and power factor correcting an ac input signal to a second acsignal; and transforming the second ac signal into a third ac signalhaving a current suitable for welding, cutting or heating.
 10. Themethod of claim 9, wherein the converting the ac input signal includesof converting the ac signal to a dc signal and inverting the dc signalto provide the second ac signal.
 11. The method of claim 10, whereininverting includes the step of pulse width modulating.
 12. The method ofclaim 10 further including rectifying the third ac signal.
 13. Themethod of claim 10 further including cycloconverting the third acsignal.
 14. The method of claim 9 further including providing controlsignals to an inverter.
 15. The method of claim 9, including providingauxiliary power signal by transforming the ac input signal.
 16. Awelding, cutting or heating power source for providing a welding,cutting or heating current from a range of input voltages, comprising:rectifier means for receiving an ac input and providing a first dcsignal; converting means for converting and power factor correcting thedc signal to a second ac signal; transforming means for transforming thesecond ac signal into a third ac signal having a current suitable forwelding, cutting or heating; and output means for providing a welding,cutting or heating current.
 17. The apparatus of claim 16, wherein themeans for converting includes means for converting the dc signal to asecond dc signal and means for inverting the second dc signal to providethe second ac signal.
 18. The apparatus of claim 16 further includingmeans for providing control signals to an inverter.
 19. The apparatus ofclaim 16, further including means for providing an auxiliary powersignal and for transforming the ac input signal into the auxiliary powersignal.
 20. The apparatus of claim 16, wherein the means for convertingthe dc signal to a second dc signal includes means for boosting thevoltage.
 21. The apparatus of claim 16, wherein the means for invertingincludes means for pulse width modulating.
 22. The apparatus of claim16, wherein the output means includes means for rectifying the third acsignal.
 23. The apparatus of claim 16, wherein the output means includesmeans for cycloconverting the third ac signal.